Coupon

Effects

On use, makes a random item in the current room that costs money or hearts free.
While held, guarantees a random item or pickup from the (Shop) Shop to be half price.

Using the Coupon in a (Devil Room) Devil Room and taking that free item does not affect or remove the chances for (Angel Room) Angel Rooms.
Using the Coupon in Greed Mode does not restock the taken item or consumable.
Using the Coupon in a Shop while holding Restock will not respawn a new item after taking the free one.
(Added in Repentance) Using the Coupon as (The Lost) The Lost or (Tainted Lost) Tainted Lost allows multiple Devil deals to be taken.

(Added in Repentance) Book of Virtues: Spawns green wisps on the middle ring. The wisps fire three tears at a time, similarly to The Inner Eye. However, all of these wisps are destroyed if Isaac buys something using money. Does not affect wisps other than ones made by this item.
Car Battery: Makes two items free upon use.
(Added in Repentance) Satanic Bible: The Devil deal in the boss room can be acquired for free.